1. Field of the Invention:
This invention relates in general to an apparatus used in drilling operations, and in particular, to an apparatus used on a rig for moving stands of pipe between the rotary and the setback or rack area.
2. Description of the Prior Art:
Rotary drilling rigs utilize sections of drill pipe and drill collars which are threaded together or "made up" when the drill stem is being placed in the hole. Conversely, the drill pipe sections and drill collars are "broken out" when the drill stem is being removed from the hole. In off-shore operations, drill pipe is lead through stands of marine riser pipe which must also be transferred and handled on the rig.
The transfer of stands of pipes between the rotary table and a setback area where the stands are racked has been a difficult and hazardous manual operation in the past. Because of the large weight of the stands of pipe great strength and physical stamina are required of the drilling crews. A serious accident could result should the crew lose control of a stand.
As a consequence, it has for years been thought desirable and advantageous to provide a mechanical device for transferring stands between the rotary and the setback or racking area in a drill rig. A mechanical system should be safer since greater strength and a more positive control is possible. A reduction in crew fatigue can be achieved. A mechanical device can be remotely operated, and as a result, safety can be enhanced. In addition, the transfer time can be decreased, thereby reducing trip time to increase efficiency.
In pursuit of the above objects, mechanical pipe handling systems for drill rigs has been available for a number of years.
A successful pipe handling system is disclosed in the publication, "1978-1979 BJ Hughes Oilfield Products and Systems" catalogue, page 308-310. The manipulators in this system consist of a number of carriages transversely aligned within the derrick, each of which includes an arm to support a pipe gripping head. Although the system is relatively simple and reliable, it requires special derrick modifications and a different racking sequence than that usually used by derrick personnel.
Golar-Nor Offshore A/S of Oslow, Norway has a system consisting of a cylinder pivotally attached by a turret to a dolly movably mounted on a track secured to the lower side of the monkeyboard in the derrick. A pipe gripping head is mounted on the end of the cylinder rod, and although the mechanism is relatively simple, it is excessively space consuming because the retracted length of the cylinder, rod and pipe gripping head is greater than the stroke of the cylinder. A better understanding of this type of device maybe seen with reference to U.S. Pat. No. 4,117,941.
Another system is shown in the pending application of Paul S. Putnam et al, entitled "Mechanized Stand Handling Apparatus for Drilling Rings", Ser. No. 833,145, filed Sep. 14, 1977 now U.S. Pat. No. 4,274,778. This system employs an articulated arm, pivotally joined in the middle, and further interconnected through linkages, gears, master-slave cylinders, or combinations thereof, so that motion of one section causes relative motion of the second section to require the pipe gripping head to travel in essentially a straight line while remaining in a horizontal position at all times. This mechanism is relatively complex and presents difficulties in decreasing size and weight, an important consideration since stresses in derricks should be minimized. The system does have the advantage, however, of retraction into a sufficiently small space and provides relatively large racking capacity at the setback, fingerboard or racking area.